A nondestructive testing technique using an X-ray has been widely used in industry to medicine. An X-ray is electromagnetic waves having a wavelength in the range of, for example, about 1 pm to 10 nm (10−12 to 10−8 m). An X-ray having a short wavelength (energy in the range of about 2 keV to 100 keV) are called hard X-rays, and X-rays having a long wavelength (energy in the range of about 0.1 keV to 2 keV) are called soft X-rays.
For example, according to an absorption contrast method that uses difference in X-ray absorptivity, the transmissivity for an X-ray is high and, therefore, the absorption contrast method is used for, for example, internal crack inspection of steel materials and security applications, such as baggage inspection. On the other hand, an X-ray phase imaging method detects a phase shift of X-rays caused by a detection object. The X-ray phase imaging method is effective for a detection object made of a low-density material, because absorption contrast of X-rays is not clearly formed by such a material.
Patent Literature 1 describes a refraction contrast method, which is an X-ray imaging method that uses a refraction effect caused by a detection object. To be specific, the refraction contrast method uses a microfocus X-ray source and takes an image of a detection object that is positioned at a distance from a detector. With this method, the edge of a detection object is detected in an enhanced manner owing to a refraction effect of X-rays caused by a detection object. Because the method uses the refraction effect, it is not necessary to use highly coherent X-rays such as synchrotron radiation, which distinguishes the method from many other X-ray phase imaging methods.